Pipes are visually checked by means of remote controlled carriages, on which cameras are mounted. Such camera carriage or dolly is disclosed for example in WO 2004/113861 A1. The camera or the several cameras mounted on the carriage for different purposes with different optical systems can be rotated, swivelled and also varied in height by means of an electric scissor linkage. The cameras generate an image stream which is evaluated. To document the ascertained sites of damage it is desirable to be able to document the location of the damaged sites. For example, from DE-A 36 05 654 a method is known in which the electrical signals from rotational angle transducers are digitally displayed on a monitor outside of the pipe. To identify the damaged site, the camera must be focused in the particular line of vision. Assessing the order of magnitude of a damaged site is only incompletely possible with this method.
To improve the evaluation capability, EP 0 623 814 A2 proposes a method for operating a drivable pipe inspection apparatus comprising a camera head swivellable about two orthogonal axes, whose swivel motion is brought about by remote-controllable motors and measured by rotational angle transducers, whose signals can be displayed and evaluated on a monitor. The measuring signals of the rotational angle transducer are supplied to electronic evaluation circuitry, which, after input or measurement of pipe-specific constants, proportional to the pipe radius and the pipe axial distance of the camera objective lens, calculates the length of the line of sight between camera objective lens and a target point on the inner surface of the pipe and, as a function of it, can determine different values by calculation by means of electronic evaluation circuitry.
In this way damaged sites could be digitally documented with respect to their position and location and their distances.
To arrive on the basis of these individual considerations of different objects at an acquisition of the entire pipe and to inspect all places of the pipe at any desired angle, EP 1 022 553 A2 proposes equipping a camera carriage with an illumination device and two electronic cameras, of which the one is located at a front end of the camera carriage and the other camera at the rear end of the camera carriage, each with a wide angle objective lens acquiring a hemispheric space, the optical axes of the two wide-angle objective lenses extending parallel to one another in the opposite direction. The recorded images of the two acquired hemispheric spaces are combined by calculation at specific time or space intervals to a spheric full image taking into consideration the distance of the optic centers of the two cameras.
The particular position of the camera units in space at the time of exposure can be acquired and stored at the time in order to compensate during the combining a roll-[axis] or inclination discrepancy of the two cameras.
Obtaining these digital fully spherical panoramic images subsequently permits virtually driving through the pipe on the basis of the stored image data, and a critical location can then be approached by calculation thereby that the corresponding spherical coordinates and stretch positions of the location to be inspected are entered.
Of disadvantage in this method is that very high computing expenditures are necessary for combining the spherical images and an especially high data stream must be supplied to the correspondingly large stores. The evaluation is divided into two steps. Immediate decisions are not possible using this method.
Since the interpretation of the image data requires a precise orientation within the pipe, and this is visually only possible in the presence of residual fluids in the pipe, GB 2 342 419 A proposes providing two different cameras, of which one is directed in the direction of the pipe for orientation and a second one radially onto the surface of the pipe. This camera directed laterally can be rotated about the longitudinal axis of the inspection head.
The disadvantage of the perspectively shortened images, which scarcely make possible the exact technical evaluation by measurement, is counteracted in DE 42 06 609 A1 with a modified camera head with two optical channels. The line of sight of the first optical channel utilized for the control of the carriage extends here in the pipe direction and that of the second optical channel, supplying the images of the inner wall of the pipe, perpendicularly to the pipe wall. The two optical channels, perpendicular to one another, of the camera head operate in different spectral ranges and are so combined via an optics assembly, for example a beam splitter, that they have a common optical axis. The images recorded by a CCD color matrix are separated again by a signal processing group into two black-and-white images, of which one contains the image information of the pipe wall and the other the image information of the second line of sight.
For better orientation DE 40 17 238 A1 describes a damage locating method and a device for locating leakages in channels with the aid of a GEO radar. For the correlation of the measurement results with the associated spatial locations, sensors for the position orientation of the carriage frame and/or of the antennas are provided. These can inter alia serve for determining the requisite location information by means of a gravitational or inertial system and should inter alia make possible measuring the stretch traversed in the pipe. The inspection results are displayed as a runtime chart. With such methods it is also possible to locate damaged sites outside of the pipe in the ground.
Of disadvantage in all methods is that an automated simple inspection of channels is not possible. The image data are generally obtained first and only evaluated quantitatively in a second step.